js/xpconnect/src/XPCJSID.cpp
author Kyle Huey <khuey@kylehuey.com>
Tue, 11 Aug 2015 06:10:46 -0700
changeset 257246 a13c1f26e351dd6251da641fe7a9eb53790fc2d0
parent 256257 65f68419dbfcefe79421876936e62c7b0a58a9df
child 266353 91d4539e00cecb658604e021675a923c60ef3235
permissions -rw-r--r--
Bug 1179909: Refactor stable state handling. r=smaug This is motivated by three separate but related problems: 1. Our concept of recursion depth is broken for things that run from AfterProcessNextEvent observers (e.g. Promises). We decrement the recursionDepth counter before firing observers, so a Promise callback running at the lowest event loop depth has a recursion depth of 0 (whereas a regular nsIRunnable would be 1). This is a problem because it's impossible to distinguish a Promise running after a sync XHR's onreadystatechange handler from a top-level event (since the former runs with depth 2 - 1 = 1, and the latter runs with just 1). 2. The nsIThreadObserver mechanism that is used by a lot of code to run "after" the current event is a poor fit for anything that runs script. First, the order the observers fire in is the order they were added, not anything fixed by spec. Additionally, running script can cause the event loop to spin, which is a big source of pain here (bholley has some nasty bug caused by this). 3. We run Promises from different points in the code for workers and main thread. The latter runs from XPConnect's nsIThreadObserver callbacks, while the former runs from a hardcoded call to run Promises in the worker event loop. What workers do is particularly problematic because it means we can't get the right recursion depth no matter what we do to nsThread. The solve this, this patch does the following: 1. Consolidate some handling of microtasks and all handling of stable state from appshell and WorkerPrivate into CycleCollectedJSRuntime. 2. Make the recursionDepth counter only available to CycleCollectedJSRuntime (and its consumers) and remove it from the nsIThreadInternal and nsIThreadObserver APIs. 3. Adjust the recursionDepth counter so that microtasks run with the recursionDepth of the task they are associated with. 4. Introduce the concept of metastable state to replace appshell's RunBeforeNextEvent. Metastable state is reached after every microtask or task is completed. This provides the semantics that bent and I want for IndexedDB, where transactions autocommit at the end of a microtask and do not "spill" from one microtask into a subsequent microtask. This differs from appshell's RunBeforeNextEvent in two ways: a) It fires between microtasks, which was the motivation for starting this. b) It no longer ensures that we're at the same event loop depth in the native event queue. bent decided we don't care about this. 5. Reorder stable state to happen after microtasks such as Promises, per HTML. Right now we call the regular thread observers, including appshell, before the main thread observer (XPConnect), so stable state tasks happen before microtasks.

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* vim: set ts=8 sts=4 et sw=4 tw=99: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* An xpcom implementation of the JavaScript nsIID and nsCID objects. */

#include "xpcprivate.h"
#include "mozilla/dom/BindingUtils.h"
#include "mozilla/Attributes.h"
#include "mozilla/jsipc/CrossProcessObjectWrappers.h"
#include "mozilla/StaticPtr.h"

using namespace mozilla::dom;
using namespace JS;

/***************************************************************************/
// nsJSID

NS_IMPL_CLASSINFO(nsJSID, nullptr, 0, NS_JS_ID_CID)
NS_IMPL_ISUPPORTS_CI(nsJSID, nsIJSID)

const char nsJSID::gNoString[] = "";

nsJSID::nsJSID()
    : mID(GetInvalidIID()),
      mNumber(const_cast<char*>(gNoString)),
      mName(const_cast<char*>(gNoString))
{
}

nsJSID::~nsJSID()
{
    if (mNumber && mNumber != gNoString)
        free(mNumber);
    if (mName && mName != gNoString)
        free(mName);
}

void nsJSID::Reset()
{
    mID = GetInvalidIID();

    if (mNumber && mNumber != gNoString)
        free(mNumber);
    if (mName && mName != gNoString)
        free(mName);

    mNumber = mName = nullptr;
}

bool
nsJSID::SetName(const char* name)
{
    MOZ_ASSERT(!mName || mName == gNoString ,"name already set");
    MOZ_ASSERT(name,"null name");
    mName = NS_strdup(name);
    return mName ? true : false;
}

NS_IMETHODIMP
nsJSID::GetName(char * *aName)
{
    if (!aName)
        return NS_ERROR_NULL_POINTER;

    if (!NameIsSet())
        SetNameToNoString();
    MOZ_ASSERT(mName, "name not set");
    *aName = NS_strdup(mName);
    return *aName ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
}

NS_IMETHODIMP
nsJSID::GetNumber(char * *aNumber)
{
    if (!aNumber)
        return NS_ERROR_NULL_POINTER;

    if (!mNumber) {
        if (!(mNumber = mID.ToString()))
            mNumber = const_cast<char*>(gNoString);
    }

    *aNumber = NS_strdup(mNumber);
    return *aNumber ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
}

NS_IMETHODIMP_(const nsID*)
nsJSID::GetID()
{
    return &mID;
}

NS_IMETHODIMP
nsJSID::GetValid(bool* aValid)
{
    if (!aValid)
        return NS_ERROR_NULL_POINTER;

    *aValid = IsValid();
    return NS_OK;
}

NS_IMETHODIMP
nsJSID::Equals(nsIJSID* other, bool* _retval)
{
    if (!_retval)
        return NS_ERROR_NULL_POINTER;

    if (!other || mID.Equals(GetInvalidIID())) {
        *_retval = false;
        return NS_OK;
    }

    *_retval = other->GetID()->Equals(mID);
    return NS_OK;
}

NS_IMETHODIMP
nsJSID::Initialize(const char* idString)
{
    if (!idString)
        return NS_ERROR_NULL_POINTER;

    if (*idString != '\0' && mID.Equals(GetInvalidIID())) {
        Reset();

        if (idString[0] == '{') {
            if (mID.Parse(idString)) {
                return NS_OK;
            }

            // error - reset to invalid state
            mID = GetInvalidIID();
        }
    }
    return NS_ERROR_FAILURE;
}

bool
nsJSID::InitWithName(const nsID& id, const char* nameString)
{
    MOZ_ASSERT(nameString, "no name");
    Reset();
    mID = id;
    return SetName(nameString);
}

// try to use the name, if no name, then use the number
NS_IMETHODIMP
nsJSID::ToString(char** _retval)
{
    if (mName && mName != gNoString)
        return GetName(_retval);

    return GetNumber(_retval);
}

const nsID&
nsJSID::GetInvalidIID() const
{
    // {BB1F47B0-D137-11d2-9841-006008962422}
    static const nsID invalid = {0xbb1f47b0, 0xd137, 0x11d2,
                                  {0x98, 0x41, 0x0, 0x60, 0x8, 0x96, 0x24, 0x22}};
    return invalid;
}

//static
already_AddRefed<nsJSID>
nsJSID::NewID(const char* str)
{
    if (!str) {
        NS_ERROR("no string");
        return nullptr;
    }

    nsRefPtr<nsJSID> idObj = new nsJSID();
    NS_ENSURE_SUCCESS(idObj->Initialize(str), nullptr);
    return idObj.forget();
}

//static
already_AddRefed<nsJSID>
nsJSID::NewID(const nsID& id)
{
    nsRefPtr<nsJSID> idObj = new nsJSID();
    idObj->mID = id;
    idObj->mName = nullptr;
    idObj->mNumber = nullptr;
    return idObj.forget();
}


/***************************************************************************/
// Class object support so that we can share prototypes of wrapper

// This class exists just so we can have a shared scriptable helper for
// the nsJSIID class. The instances implement their own helpers. But we
// needed to be able to indicate to the shared prototypes this single flag:
// nsIXPCScriptable::DONT_ENUM_STATIC_PROPS. And having a class to do it is
// the only means we have. Setting this flag on any given instance scriptable
// helper is not sufficient to convey the information that we don't want
// static properties enumerated on the shared proto.

class SharedScriptableHelperForJSIID final : public nsIXPCScriptable
{
    ~SharedScriptableHelperForJSIID() {}
public:
    NS_DECL_ISUPPORTS
    NS_DECL_NSIXPCSCRIPTABLE
    SharedScriptableHelperForJSIID() {}
};

NS_INTERFACE_MAP_BEGIN(SharedScriptableHelperForJSIID)
  NS_INTERFACE_MAP_ENTRY(nsIXPCScriptable)
  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIXPCScriptable)
NS_INTERFACE_MAP_END

NS_IMPL_ADDREF(SharedScriptableHelperForJSIID)
NS_IMPL_RELEASE(SharedScriptableHelperForJSIID)

// The nsIXPCScriptable map declaration that will generate stubs for us...
#define XPC_MAP_CLASSNAME           SharedScriptableHelperForJSIID
#define XPC_MAP_QUOTED_CLASSNAME   "JSIID"
#define XPC_MAP_FLAGS               nsIXPCScriptable::ALLOW_PROP_MODS_DURING_RESOLVE
#include "xpc_map_end.h" /* This will #undef the above */

static mozilla::StaticRefPtr<nsIXPCScriptable> gSharedScriptableHelperForJSIID;
static bool gClassObjectsWereInited = false;

static void EnsureClassObjectsInitialized()
{
    if (!gClassObjectsWereInited) {
        gSharedScriptableHelperForJSIID = new SharedScriptableHelperForJSIID();

        gClassObjectsWereInited = true;
    }
}

NS_METHOD GetSharedScriptableHelperForJSIID(nsIXPCScriptable** helper)
{
    EnsureClassObjectsInitialized();
    nsCOMPtr<nsIXPCScriptable> temp = gSharedScriptableHelperForJSIID.get();
    temp.forget(helper);
    return NS_OK;
}

/******************************************************/

#define NULL_CID                                                              \
{ 0x00000000, 0x0000, 0x0000,                                                 \
  { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }

// We pass nsIClassInfo::DOM_OBJECT so that nsJSIID instances may be created
// in unprivileged scopes.
NS_DECL_CI_INTERFACE_GETTER(nsJSIID)
NS_IMPL_CLASSINFO(nsJSIID, GetSharedScriptableHelperForJSIID,
                  nsIClassInfo::DOM_OBJECT, NULL_CID)

NS_DECL_CI_INTERFACE_GETTER(nsJSCID)
NS_IMPL_CLASSINFO(nsJSCID, nullptr, 0, NULL_CID)

void xpc_DestroyJSxIDClassObjects()
{
    if (gClassObjectsWereInited) {
        NS_IF_RELEASE(NS_CLASSINFO_NAME(nsJSIID));
        NS_IF_RELEASE(NS_CLASSINFO_NAME(nsJSCID));
        gSharedScriptableHelperForJSIID = nullptr;

        gClassObjectsWereInited = false;
    }
}

/***************************************************************************/

NS_INTERFACE_MAP_BEGIN(nsJSIID)
  NS_INTERFACE_MAP_ENTRY(nsIJSID)
  NS_INTERFACE_MAP_ENTRY(nsIJSIID)
  NS_INTERFACE_MAP_ENTRY(nsIXPCScriptable)
  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIJSID)
  NS_IMPL_QUERY_CLASSINFO(nsJSIID)
NS_INTERFACE_MAP_END

NS_IMPL_ADDREF(nsJSIID)
NS_IMPL_RELEASE(nsJSIID)
NS_IMPL_CI_INTERFACE_GETTER(nsJSIID, nsIJSID, nsIJSIID)

// The nsIXPCScriptable map declaration that will generate stubs for us...
#define XPC_MAP_CLASSNAME           nsJSIID
#define XPC_MAP_QUOTED_CLASSNAME   "nsJSIID"
#define                             XPC_MAP_WANT_RESOLVE
#define                             XPC_MAP_WANT_ENUMERATE
#define                             XPC_MAP_WANT_HASINSTANCE
#define XPC_MAP_FLAGS               nsIXPCScriptable::ALLOW_PROP_MODS_DURING_RESOLVE
#include "xpc_map_end.h" /* This will #undef the above */


nsJSIID::nsJSIID(nsIInterfaceInfo* aInfo)
    : mInfo(aInfo)
{
}

nsJSIID::~nsJSIID() {}

// If mInfo is present we use it and ignore mDetails, else we use mDetails.

NS_IMETHODIMP nsJSIID::GetName(char * *aName)
{
    return mInfo->GetName(aName);
}

NS_IMETHODIMP nsJSIID::GetNumber(char * *aNumber)
{
    char str[NSID_LENGTH];
    const nsIID* id;
    mInfo->GetIIDShared(&id);
    id->ToProvidedString(str);
    *aNumber = (char*) nsMemory::Clone(str, NSID_LENGTH);
    return *aNumber ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
}

NS_IMETHODIMP_(const nsID*) nsJSIID::GetID()
{
    const nsIID* id;
    mInfo->GetIIDShared(&id);
    return id;
}

NS_IMETHODIMP nsJSIID::GetValid(bool* aValid)
{
    *aValid = true;
    return NS_OK;
}

NS_IMETHODIMP nsJSIID::Equals(nsIJSID* other, bool* _retval)
{
    if (!_retval)
        return NS_ERROR_NULL_POINTER;

    if (!other) {
        *_retval = false;
        return NS_OK;
    }

    mInfo->IsIID(other->GetID(), _retval);
    return NS_OK;
}

NS_IMETHODIMP nsJSIID::Initialize(const char* idString)
{
    return NS_ERROR_FAILURE;
}

NS_IMETHODIMP nsJSIID::ToString(char** _retval)
{
    return mInfo->GetName(_retval);
}

// static
already_AddRefed<nsJSIID>
nsJSIID::NewID(nsIInterfaceInfo* aInfo)
{
    if (!aInfo) {
        NS_ERROR("no info");
        return nullptr;
    }

    bool canScript;
    if (NS_FAILED(aInfo->IsScriptable(&canScript)) || !canScript)
        return nullptr;

    nsRefPtr<nsJSIID> idObj = new nsJSIID(aInfo);
    return idObj.forget();
}


NS_IMETHODIMP
nsJSIID::Resolve(nsIXPConnectWrappedNative* wrapper,
                 JSContext * cx, JSObject * objArg,
                 jsid idArg, bool* resolvedp,
                 bool* _retval)
{
    RootedObject obj(cx, objArg);
    RootedId id(cx, idArg);
    XPCCallContext ccx(JS_CALLER, cx);

    AutoMarkingNativeInterfacePtr iface(ccx);

    iface = XPCNativeInterface::GetNewOrUsed(mInfo);

    if (!iface)
        return NS_OK;

    XPCNativeMember* member = iface->FindMember(id);
    if (member && member->IsConstant()) {
        RootedValue val(cx);
        if (!member->GetConstantValue(ccx, iface, val.address()))
            return NS_ERROR_OUT_OF_MEMORY;

        *resolvedp = true;
        *_retval = JS_DefinePropertyById(cx, obj, id, val,
                                         JSPROP_ENUMERATE | JSPROP_READONLY |
                                         JSPROP_PERMANENT | JSPROP_RESOLVING);
    }

    return NS_OK;
}

NS_IMETHODIMP
nsJSIID::Enumerate(nsIXPConnectWrappedNative* wrapper,
                   JSContext * cx, JSObject * objArg, bool* _retval)
{
    // In this case, let's just eagerly resolve...

    RootedObject obj(cx, objArg);
    XPCCallContext ccx(JS_CALLER, cx);

    AutoMarkingNativeInterfacePtr iface(ccx);

    iface = XPCNativeInterface::GetNewOrUsed(mInfo);

    if (!iface)
        return NS_OK;

    uint16_t count = iface->GetMemberCount();
    for (uint16_t i = 0; i < count; i++) {
        XPCNativeMember* member = iface->GetMemberAt(i);
        if (member && member->IsConstant() &&
            !xpc_ForcePropertyResolve(cx, obj, member->GetName())) {
            return NS_ERROR_UNEXPECTED;
        }
    }
    return NS_OK;
}

/*
 * HasInstance hooks need to find an appropriate reflector in order to function
 * properly. There are two complexities that we need to handle:
 *
 * 1 - Cross-compartment wrappers. Chrome uses over 100 compartments, all with
 *     system principal. The success of an instanceof check should not depend
 *     on which compartment an object comes from. At the same time, we want to
 *     make sure we don't unwrap important security wrappers.
 *     CheckedUnwrap does the right thing here.
 *
 * 2 - Prototype chains. Suppose someone creates a vanilla JS object |a| and
 *     sets its __proto__ to some WN |b|. If |b instanceof nsIFoo| returns true,
 *     one would expect |a instanceof nsIFoo| to return true as well, since
 *     instanceof is transitive up the prototype chain in ECMAScript. Moreover,
 *     there's chrome code that relies on this.
 *
 * This static method handles both complexities, returning either an XPCWN, a
 * DOM object, or null. The object may well be cross-compartment from |cx|.
 */
static JSObject*
FindObjectForHasInstance(JSContext* cx, HandleObject objArg)
{
    RootedObject obj(cx, objArg), proto(cx);

    while (obj && !IS_WN_REFLECTOR(obj) &&
           !IsDOMObject(obj) && !mozilla::jsipc::IsCPOW(obj))
    {
        if (js::IsWrapper(obj)) {
            obj = js::CheckedUnwrap(obj, /* stopAtOuter = */ false);
            continue;
        }
        if (!js::GetObjectProto(cx, obj, &proto))
            return nullptr;
        obj = proto;
    }
    return obj;
}

nsresult
xpc::HasInstance(JSContext* cx, HandleObject objArg, const nsID* iid, bool* bp)
{
    *bp = false;

    RootedObject obj(cx, FindObjectForHasInstance(cx, objArg));
    if (!obj)
        return NS_OK;

    if (mozilla::jsipc::IsCPOW(obj))
        return mozilla::jsipc::InstanceOf(obj, iid, bp);

    nsISupports* identity = UnwrapReflectorToISupports(obj);
    if (!identity)
        return NS_OK;

    nsCOMPtr<nsISupports> supp;
    identity->QueryInterface(*iid, getter_AddRefs(supp));
    *bp = supp;

    // Our old HasInstance implementation operated by invoking FindTearOff on
    // XPCWrappedNatives, and various bits of chrome JS came to depend on
    // |instanceof| doing an implicit QI if it succeeds. Do a drive-by QI to
    // preserve that behavior. This is just a compatibility hack, so we don't
    // really care if it fails.
    if (IS_WN_REFLECTOR(obj))
        (void) XPCWrappedNative::Get(obj)->FindTearOff(*iid);

    return NS_OK;
}

NS_IMETHODIMP
nsJSIID::HasInstance(nsIXPConnectWrappedNative* wrapper,
                     JSContext* cx, JSObject * /* unused */,
                     HandleValue val, bool* bp, bool* _retval)
{
    *bp = false;

    if (val.isPrimitive())
        return NS_OK;

    // we have a JSObject
    RootedObject obj(cx, &val.toObject());

    const nsIID* iid;
    mInfo->GetIIDShared(&iid);
    return xpc::HasInstance(cx, obj, iid, bp);
}

/***************************************************************************/

NS_INTERFACE_MAP_BEGIN(nsJSCID)
  NS_INTERFACE_MAP_ENTRY(nsIJSID)
  NS_INTERFACE_MAP_ENTRY(nsIJSCID)
  NS_INTERFACE_MAP_ENTRY(nsIXPCScriptable)
  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIJSID)
  NS_IMPL_QUERY_CLASSINFO(nsJSCID)
NS_INTERFACE_MAP_END

NS_IMPL_ADDREF(nsJSCID)
NS_IMPL_RELEASE(nsJSCID)
NS_IMPL_CI_INTERFACE_GETTER(nsJSCID, nsIJSID, nsIJSCID)

// The nsIXPCScriptable map declaration that will generate stubs for us...
#define XPC_MAP_CLASSNAME           nsJSCID
#define XPC_MAP_QUOTED_CLASSNAME   "nsJSCID"
#define                             XPC_MAP_WANT_CONSTRUCT
#define                             XPC_MAP_WANT_HASINSTANCE
#define XPC_MAP_FLAGS               0
#include "xpc_map_end.h" /* This will #undef the above */

nsJSCID::nsJSCID()  { mDetails = new nsJSID(); }
nsJSCID::~nsJSCID() {}

NS_IMETHODIMP nsJSCID::GetName(char * *aName)
    {ResolveName(); return mDetails->GetName(aName);}

NS_IMETHODIMP nsJSCID::GetNumber(char * *aNumber)
    {return mDetails->GetNumber(aNumber);}

NS_IMETHODIMP_(const nsID*) nsJSCID::GetID()
    {return &mDetails->ID();}

NS_IMETHODIMP nsJSCID::GetValid(bool* aValid)
    {return mDetails->GetValid(aValid);}

NS_IMETHODIMP nsJSCID::Equals(nsIJSID* other, bool* _retval)
    {return mDetails->Equals(other, _retval);}

NS_IMETHODIMP nsJSCID::Initialize(const char* idString)
    {return mDetails->Initialize(idString);}

NS_IMETHODIMP nsJSCID::ToString(char** _retval)
    {ResolveName(); return mDetails->ToString(_retval);}

void
nsJSCID::ResolveName()
{
    if (!mDetails->NameIsSet())
        mDetails->SetNameToNoString();
}

//static
already_AddRefed<nsJSCID>
nsJSCID::NewID(const char* str)
{
    if (!str) {
        NS_ERROR("no string");
        return nullptr;
    }

    nsRefPtr<nsJSCID> idObj = new nsJSCID();
    if (str[0] == '{') {
        NS_ENSURE_SUCCESS(idObj->Initialize(str), nullptr);
    } else {
        nsCOMPtr<nsIComponentRegistrar> registrar;
        NS_GetComponentRegistrar(getter_AddRefs(registrar));
        NS_ENSURE_TRUE(registrar, nullptr);

        nsCID* cid;
        if (NS_FAILED(registrar->ContractIDToCID(str, &cid)))
            return nullptr;
        bool success = idObj->mDetails->InitWithName(*cid, str);
        free(cid);
        if (!success)
            return nullptr;
    }
    return idObj.forget();
}

static const nsID*
GetIIDArg(uint32_t argc, const JS::Value& val, JSContext* cx)
{
    const nsID* iid;

    // If an IID was passed in then use it
    if (argc) {
        JSObject* iidobj;
        if (val.isPrimitive() ||
            !(iidobj = val.toObjectOrNull()) ||
            !(iid = xpc_JSObjectToID(cx, iidobj))) {
            return nullptr;
        }
    } else
        iid = &NS_GET_IID(nsISupports);

    return iid;
}

NS_IMETHODIMP
nsJSCID::CreateInstance(HandleValue iidval, JSContext* cx,
                        uint8_t optionalArgc, MutableHandleValue retval)
{
    if (!mDetails->IsValid())
        return NS_ERROR_XPC_BAD_CID;

    if (NS_FAILED(nsXPConnect::SecurityManager()->CanCreateInstance(cx, mDetails->ID()))) {
        NS_ERROR("how are we not being called from chrome here?");
        return NS_OK;
    }

    // If an IID was passed in then use it
    const nsID* iid = GetIIDArg(optionalArgc, iidval, cx);
    if (!iid)
        return NS_ERROR_XPC_BAD_IID;

    nsCOMPtr<nsIComponentManager> compMgr;
    nsresult rv = NS_GetComponentManager(getter_AddRefs(compMgr));
    if (NS_FAILED(rv))
        return NS_ERROR_UNEXPECTED;

    nsCOMPtr<nsISupports> inst;
    rv = compMgr->CreateInstance(mDetails->ID(), nullptr, *iid, getter_AddRefs(inst));
    MOZ_ASSERT(NS_FAILED(rv) || inst, "component manager returned success, but instance is null!");

    if (NS_FAILED(rv) || !inst)
        return NS_ERROR_XPC_CI_RETURNED_FAILURE;

    rv = nsContentUtils::WrapNative(cx, inst, iid, retval);
    if (NS_FAILED(rv) || retval.isPrimitive())
        return NS_ERROR_XPC_CANT_CREATE_WN;
    return NS_OK;
}

NS_IMETHODIMP
nsJSCID::GetService(HandleValue iidval, JSContext* cx, uint8_t optionalArgc,
                    MutableHandleValue retval)
{
    if (!mDetails->IsValid())
        return NS_ERROR_XPC_BAD_CID;

    if (NS_FAILED(nsXPConnect::SecurityManager()->CanCreateInstance(cx, mDetails->ID()))) {
        MOZ_ASSERT(JS_IsExceptionPending(cx),
                   "security manager vetoed GetService without setting exception");
        return NS_OK;
    }

    // If an IID was passed in then use it
    const nsID* iid = GetIIDArg(optionalArgc, iidval, cx);
    if (!iid)
        return NS_ERROR_XPC_BAD_IID;

    nsCOMPtr<nsIServiceManager> svcMgr;
    nsresult rv = NS_GetServiceManager(getter_AddRefs(svcMgr));
    if (NS_FAILED(rv))
        return rv;

    nsCOMPtr<nsISupports> srvc;
    rv = svcMgr->GetService(mDetails->ID(), *iid, getter_AddRefs(srvc));
    MOZ_ASSERT(NS_FAILED(rv) || srvc, "service manager returned success, but service is null!");
    if (NS_FAILED(rv) || !srvc)
        return NS_ERROR_XPC_GS_RETURNED_FAILURE;

    RootedValue v(cx);
    rv = nsContentUtils::WrapNative(cx, srvc, iid, &v);
    if (NS_FAILED(rv) || !v.isObject())
        return NS_ERROR_XPC_CANT_CREATE_WN;

    retval.set(v);
    return NS_OK;
}

NS_IMETHODIMP
nsJSCID::Construct(nsIXPConnectWrappedNative* wrapper,
                   JSContext* cx, JSObject* objArg,
                   const CallArgs& args, bool* _retval)
{
    RootedObject obj(cx, objArg);
    XPCJSRuntime* rt = nsXPConnect::GetRuntimeInstance();
    if (!rt)
        return NS_ERROR_FAILURE;

    // 'push' a call context and call on it
    RootedId name(cx, rt->GetStringID(XPCJSRuntime::IDX_CREATE_INSTANCE));
    XPCCallContext ccx(JS_CALLER, cx, obj, nullptr, name, args.length(), args.array(),
                       args.rval().address());

    *_retval = XPCWrappedNative::CallMethod(ccx);
    return NS_OK;
}

NS_IMETHODIMP
nsJSCID::HasInstance(nsIXPConnectWrappedNative* wrapper,
                     JSContext* cx, JSObject * /* unused */,
                     HandleValue val, bool* bp, bool* _retval)
{
    *bp = false;
    nsresult rv = NS_OK;

    if (val.isObject()) {
        // we have a JSObject
        RootedObject obj(cx, &val.toObject());

        MOZ_ASSERT(obj, "when is an object not an object?");

        // is this really a native xpcom object with a wrapper?
        nsIClassInfo* ci = nullptr;
        obj = FindObjectForHasInstance(cx, obj);
        if (!obj || !IS_WN_REFLECTOR(obj))
            return rv;
        if (XPCWrappedNative* other_wrapper = XPCWrappedNative::Get(obj))
            ci = other_wrapper->GetClassInfo();

        // We consider CID equality to be the thing that matters here.
        // This is perhaps debatable.
        if (ci) {
            nsID cid;
            if (NS_SUCCEEDED(ci->GetClassIDNoAlloc(&cid)))
                *bp = cid.Equals(mDetails->ID());
        }
    }

    return rv;
}

/***************************************************************************/
// additional utilities...

JSObject*
xpc_NewIDObject(JSContext* cx, HandleObject jsobj, const nsID& aID)
{
    RootedObject obj(cx);

    nsCOMPtr<nsIJSID> iid = nsJSID::NewID(aID);
    if (iid) {
        nsXPConnect* xpc = nsXPConnect::XPConnect();
        if (xpc) {
            xpc->WrapNative(cx, jsobj, static_cast<nsISupports*>(iid),
                            NS_GET_IID(nsIJSID), obj.address());
        }
    }
    return obj;
}

// note: returned pointer is only valid while |obj| remains alive!
const nsID*
xpc_JSObjectToID(JSContext* cx, JSObject* obj)
{
    if (!cx || !obj)
        return nullptr;

    // NOTE: this call does NOT addref
    XPCWrappedNative* wrapper = nullptr;
    obj = js::CheckedUnwrap(obj);
    if (obj && IS_WN_REFLECTOR(obj))
        wrapper = XPCWrappedNative::Get(obj);
    if (wrapper &&
        (wrapper->HasInterfaceNoQI(NS_GET_IID(nsIJSID))  ||
         wrapper->HasInterfaceNoQI(NS_GET_IID(nsIJSIID)) ||
         wrapper->HasInterfaceNoQI(NS_GET_IID(nsIJSCID)))) {
        return ((nsIJSID*)wrapper->GetIdentityObject())->GetID();
    }
    return nullptr;
}

bool
xpc_JSObjectIsID(JSContext* cx, JSObject* obj)
{
    MOZ_ASSERT(cx && obj, "bad param");
    // NOTE: this call does NOT addref
    XPCWrappedNative* wrapper = nullptr;
    obj = js::CheckedUnwrap(obj);
    if (obj && IS_WN_REFLECTOR(obj))
        wrapper = XPCWrappedNative::Get(obj);
    return wrapper &&
           (wrapper->HasInterfaceNoQI(NS_GET_IID(nsIJSID))  ||
            wrapper->HasInterfaceNoQI(NS_GET_IID(nsIJSIID)) ||
            wrapper->HasInterfaceNoQI(NS_GET_IID(nsIJSCID)));
}